The production of linear, aromatic polyphosphonates by condensing aryl phosphonic acid dichlorides and aromatic diols in a solvent in the absence of a catalyst or in the presence of alkaline-earth metal halide catalysts is a known process and is described in several U.S. Patens (see e.g., U.S. Pat. Nos. 2,534,252; 3,946,093; 3,919,363 and 6,288210 B1). The polyphosphonates are isolated from the solutions by precipitation into methanol or by evaporation of the solvent. Polyphosphonates are known to exhibit excellent fire resistance (see e.g., U.S. Pat. Nos. 2,682,522, 2,891,915 and 4,331,614). It is know (see e.g., U.S. Pat. No. 2,682,522) that linear polyphosphonates can be produced by melt condensing a phosphonic acid diaryl ester and a bisphenol using a metal catalyst (e.g., sodium phenolate) at high temperature. This approach produced low molecular weight polyphosphonates that exhibited poor toughness.
Consequently, to improve toughness a synthetic approach to produce branched polyphosphonates by the transesterification process was developed (see e.g., U.S. Pat. No. 4,331,614). This approach involved the transesterification reaction of a phosphonic acid diaryl ester, a bisphenol, a branching agent (tri or tetra phenol or phosphonic acid ester), and a preferred catalyst (e.g., sodium phenolate) carried out in the melt, usually in an autoclave. Several patents have addressed the use of branching agents in polyphosphonates (see e.g., U.S. Pat. Nos. 2,716,101; 3,326,852; 4,328,174; 4,331,614; 4,374,971; 4,415,719; 5,216,113; 5,334,692; and 4,374,971). These approaches have met with some degree of success, however, the combination of properties exhibited by these polyphosphonates are still not sufficient for general acceptance in the marketplace. For example in branched polyphosphonates, the number average molecular weights as high as 200,000 g/mole are claimed with a minimum requirement of 11,000 g/mole (see e.g., U.S. Pat. No. 4,331,614) with polymer dispersities less than 2.5. Consequently these polyphosphonates exhibited high melt viscosities. This approach was successful in producing high molecular weight polyphosphonates that exhibited improved toughness, but processability was sacrificed. Another disadvantage for this process is that it requires high purity monomers, preferably greater than 99.7% (see e.g., U.S. Pat. No. 4,331,614) that make it expensive. Another shortcoming of both the linear and branched polyphosphonates was the lack of hydrolytic stability and haze.
Recently, the development of a method to produce branched polyphosphonates with superior combination of properties was disclosed (“Branched Polyphosphonates that Exhibit an Advantageous Combination of Properties, and Methods Related Thereto”, 2004 0167284 A1, published Aug. 26, 2004, Ser. No. 10/374829, filing date Feb. 24, 2003). In practice, these materials are stable for more than 5 hours at 300° C. under vacuum (<0.5 mm Hg) but can experience degradation upon exposure to high temperature (>250° C.) and air, air (oxygen), moisture or combinations thereof. The polyphosphonates are exposed to such conditions not during the final stages of synthesis, but when melt mixing with other polymers or during molding processes. The degradation is manifested by reduction in molecular weight that in turn causes loss of mechanical properties such as strength, modulus and toughness. In addition, the fire resistance is negatively affected by this reduction in molecular weight. As the molecular weight decreases, the melt flow of the material increases so that in a flame, the material propensity to drip increases significantly. Thus, additives that can prevent any unwanted degradation of polyphosphonates during thermal treatment are needed.
A list of patents on both linear and branched polyphosphonates is provided below.
                1. U.S. Pat. No. 2,435,252 (1948 A. D. F. Toy, et al., Victor Chemical Works)        2. U.S. Pat. No. 2,682,522 (1954 H. W. Coover, et al., Eastman Kodak)        3. U.S. Pat. No. 2,716,101 (1955 H. W. Coover, et al., Eastman Kodak)        4. U.S. Pat. No. 2,891,915 (1959 W. B. McCormack, et al., DuPont)        5. U.S. Pat. No. 3,326,852 (1967 I. M. Thomas, et al., Owens Illinois, Inc)        6. U.S. Pat. No. 3,719,727 (1973 Y. Masai, et al., Toyo Spinning Co.)        7. U.S. Pat. No. 3,829,405 (1974 S. L. Cohen, et al., Fiber Industries and Celanese Corp)        8. U.S. Pat. No. 3,830,771 (1974 S. L. Cohen, et al., Fiber Industries and Celanese Corp)        9. U.S. Pat. No. 3,925,303 (1975 A. Rio, et al., Rhone-Poulec)        10. U.S. Pat. No. 3,932,351 (1976 H. L. King, et al., Monsanto)        11. U.S. Pat. No. 4,033,927 (1977 F. H. Borman, et al., General Electric)        12. U.S. Pat. No. 4,152,373 (1979 M. L. Honig, et al., Stauffer Chemical Co.)        13. U.S. Pat. No. 4,223,104 (1980 K. S. Kim, et al., Stauffer Chemical Co.)        14. U.S. Pat. No. 4,229,552 (1980 M. Shiozaki, et al., Nissan Chemical Industries, Ltd.)        15. U.S. Pat. No. 4,322,530 (1982 M. Schmidt, et al., Bayer AG)        16. U.S. Pat. No. 4,331,614 (1982 M. Schmidt, et al., Bayer AG)        17. U.S. Pat. No. 4,332,921 (1982 M. Schmidt, et al., Bayer AG)        18. U.S. Pat. No. 4,401,802 (1983 M. Schmidt, et al., Bayer AG)        19. U.S. Pat. No. 4,408,033 (1983 R. E. Hefner, et al., Dow Chemical Co)        20. U.S. Pat. No. 4,415,719, (1983 M. Schmidt, et al., Bayer AG)        21. U.S. Pat. No. 4,474,937 (1984 S. E. Bales, et al., Dow Chemical Co.)        22. U.S. Pat. No. 4,322,520 (1982, M. Schmidt, et al., Bayer AG)        23. U.S. Pat. No. 4,328,174 (1982, M. Schmidt, et al., Bayer AG)        24. U.S. Pat. No. 4,374,971 (1983, M. Schmidt, et al., Bayer AG)        25. U.S. Pat. No. 4,481,350 (1984, M. Schmidt, et al., Bayer AG)        26. U.S. Pat. No. 4,508,890 (1985, M. Schmidt, et al., Bayer AG)        27. U.S. Pat. No. 4,719,279 (1988, H. Kauth, et al., Bayer AG)        28. U.S. Pat. No. 4,762,905 (1988, M. Schmidt, et al., Bayer AG)        29. U.S. Pat. No. 4,782,123 (1988, H. Kauth, et al., Bayer AG)        30. U.S. Pat. No. 5,334,694 (1994, H. Jung, et al., Bayer AG)        
Additives have been designed for use with specific plastics to provide protection from degradation due to exposure to high temperature (>250° C.) and air, air (oxygen), moisture or combinations thereof. A wide variety of additives are commercially available, for example Ultranox Phosphite antioxidants, General Electric Specialty Materials, Morgantown, W. Va.; Irgafos Phosphites, and Irganox Phenolics, Ciba Specialty Chemicals, USA. However, since polyphosphonates with a desirable combination of properties were heretofor unknown materials, no additives have been specifically designed for use with these polymers. Therefore, it is not obvious which, if any, of the available additives will provide protection to polyphosphonates from degradation due to exposure to high temperature (>250° C.) and air, air (oxygen), moisture or combinations thereof.